Thick-film positive DUV photoresist for implant layer application

A thick positive chemical amplified DUV photoresist, Shipley UV 25, is designed with high transparency (0.18AU) for implant layer application. Comparing with traditional Novolak I-line implant layer resists high aspect ratio and fast photospeed of UV 25 is demonstrated. Lithographic results show that UV 25 has excellent coating capability up to 3 microns thick, with excellent photospeed and good overall lithographic performance for various features. Process optimizations of UV 25 for various features are investigated. The results indicate that the temperatures of softbake and post exposure-bake play very important roles in improving the process windows. We have found that high softbake for better annealing and solvent removal is critical, and the best lithographic process is typically at PEB temperatures lower than the softbake temperature (at least 20 degrees Celsius lower). The process with a high softbake temperature and a low PEB temperature significantly improved overall process window. In addition, PED stability with an optimal baking process is also studied.